How do I get file such as texture out of already packed blender file?
You can either go in the UV/Image Editor, and, in the bottom horizontal menu, select the image you want to save un the drop-down menu, then Image menu > Save As Image... or in the Node Editor, click on the Open (now Unpack) button of the Image Texture node: as the images have been packed, this button will unpack the image the way you want